Staphylococcus aureus (S. aureus) can be a virulent pathogen of animals and humans. It can also cause severe food poisoning by the production of a toxin. Diseases caused by S. aureus cover a very wide clinical spectrum, from simple skin infections to life threatening infections of the bones, heart, and organs. Of particular concern is the recognition that S. aureus infection is common after surgery. It is also associated with intravenous tubing and other implants.
The bacterium S. aureus may be transmitted between healthy individuals by skin to skin contact, or from a commonly shared item or a surface (e.g., tanning beds, gym equipment, food handling equipment, etc.) where the transfer may be made to a subsequent person who uses the shared item or touches the surface. Of great medical concern is the recognition that healthy people entering hospitals may “carry” S. aureus (e.g., on their skin, in their noses, etc.) without any signs or symptoms. In the presence of favorable conditions (often found in, but not limited to hospitals), the S. aureus can activate and cause serious infection. In addition, S. aureus can also be a source of food poisoning, often caused by a food handler contaminating the food product.
There are two broad categories of S. aureus based on an individual clone's susceptibility to a class of B. lactam antibiotics that includes methicillin. These are methicillin susceptible S. aureus (MSSA), and methicillin resistant S. aureus (MRSA). Until only a few years ago, various strains of MRSA were almost exclusively found in hospitals. Now, many are also present in the noses, skin, etc. of people in the non-hospital community. Moreover, these MRSA strains are increasingly causing serious infections in the community. MRSA is particularly serious because very few antibiotics (e.g., vancomycin) have been shown to be uniformly effective against MRSA.
The Center for Disease Control and Prevention actively surveys for the development of methicillin resistant S. aureus. In 2000, the Society for Healthcare Epidemiology of America guidelines recommended contact isolation for patients with MRSA. In addition to the morbidity and mortality caused by MRSA, it has been estimated that each case of infection costs at least $23,000.
Methicillin-susceptible Staphylococcus aureus (MSSA) and Methicillin-resistant Staphylococcus aureus (MRSA) are increasingly infecting people worldwide in both hospitals and within the community. The rate of infections in ICUs is especially troubling, rising from 2% in 1974 to 64% in 2004. One in three people carry MSSA while one in 100 people carry MRSA.